1. Field of the Invention
The present invention relates to a dye sensitized solar cell, and a method for manufacturing the dye sensitized solar cell.
2. Description of the Related Art
The general structure of a dye sensitized solar cell has been described in Jpn. Pat. Appln. KOKAI Publication No. 1-220380. The solar cell comprises an electrode containing a transparent semiconductor layer, which comprises fine particles of a metal oxide on the surface of which a dye is retained, a transparent electrode facing the electrode above, and a fluid carrier movement layer interposed between the electrodes. Such solar cells are called wet type dye sensitized solar cells because the carrier movement layer is a liquid.
A dye sensitized solar cell works through the following process. An incident light from the transparent electrode side arrives at a dye retained on the surface of the transparent semiconductor surface, and excites the dye. The excited dye promptly transfers electrons to the transparent semiconductor layer. The dye, positively charged by donor electrons, is electrically neutralized upon transfer of electrons from ions diffused from the carrier movement layer. The ions that have delivered the electrons are diffused into the transparent electrode so as to recieve electrons. The wet type dye sensitized solar cell works by using the oxide electrode and the opposing transparent electrode as a negative electrode and positive electrode, respectively.
A low molecular weight solvent is used in the wet type dye sensitized solar cell. Sealing should be strictly performed in order to prevent the liquid from leaking. However, it is difficult to maintain such shielding for months or years. Solvent loss due to evaporation of solvent molecules and leakage of the liquid may cause deterioration of the solar cell function, or the environment may be polluted. Considering the above drawbacks, instead of the fluid carrier movement layer, use of a solid electrolyte that manifests ionic conductivity and contains no solvent, or use of a solid organic material that manifests electronic conductivity, has been proposed. Such a solar cell is called a full-solid type dye sensitized solar cell.
Although there is no possibility of leakage of the liquid in these cells, they involve a problem of low energy conversion efficiency, which is thought to be caused by (1) increase of electrical resistance, (2) insufficient contact between TiO2 and electrolytes due to insufficient infusion of the solid electrolyte into interstices among the TiO2 particles, and (3) readily peeled junction interfaces between the semiconductor electrode and solid conductive material during heat cycles because the semiconductor electrode has a different thermal expansion coefficient from that of the solid conductive material.